2010 is becoming the year of the heatwave, with record temperatures set in 17 countries.

Record highs have occurred in Russia, Belarus and Ukraine – the three nations at the centre of the eastern European heatwave which has lasted for more than three weeks – but also African, Middle Eastern and Latin American countries.

Temperatures in Moscow, which have been consistently 20C above normal, today fell to 31C (86F), and President Dmitry Medvedev cancelled a state of emergency in three out of seven Russian regions affected by forest fires.

Thousand of hectares of forest burned in the fires, killing 54 people and leaving thousands homeless. For days, Moscow was shrouded in smog, and environmentalists raised fears that the blaze could release radioactive particles from areas contaminated in the 1986 Chernobyl disaster.

Wildfires have also swept through northern Portugal, killing two firefighters and destroying 18,000 hectares (44,500 acres) of forests and bushland since late July. Some 600 firefighters were today struggling to contain 29 separate fires.

But the extreme heat experienced in Europe would barely have registered in Iraq, Saudi Arabia, Niger, Pakistan and Sudan, all of which have recorded temperatures of more than 47C (115F) since June. The number of record highs is itself a record – the previous record was for 14 new high temperatures in 2007.

The freak weather conditions, which have devastated crops and wildlife, are believed to have killed thousands of elderly people, especially in Russia and northern India. The 2003 European heatwave killed about 15,000 people.

Pakistan, now experiencing its worst ever floods, had Asia's hottest day in its history on 26 May, when 53.5C (128.3F) was recorded in Mohenjo-daro, according to the Pakistani Meteorological Department. The heatwaves have also been occurring in the US, where Las Vegas, Atlantic City, Washington, Baltimore and Trenton all documented their highest ever temperatures in July.

The global research, collated by meteorologists at weather information provider Weather Underground, supports US government data collated on 11 different indicators – from air and sea temperatures to melting ice – which showed temperatures rising around the world since the 1850s. This June was also the hottest ever on record and 2010 is on course to be the warmest year since records began, according to separate data from the US National Oceanic and Atmospheric Administration published last month.

Only one country has set a record for its coldest-ever temperature in 2010. Guinea, in west Africa, recorded 1.4C (34.5F) in a nine-day cold snap at Mali-ville in the Labe region in January. Farmers lost most of their crops and animals.